If you look at a handbook of organic substances, you will find than the density of organic liquids is around 800-1200 kg/m3. It means that the density of amorphour resins will be similar. The density range you are looking for is rather that of compressed gases. So many "free volume" cannot exist is a liquid or in s solid structure without microvoid formation. Perhaps some very rigid chlatrate structure might provide low density but at this level ad the structure would be very fragile.